 Let us come to the basic fundamentals of ladder-than-air systems. Now you will see a picture here or you will see a collage of pictures here and I want you to observe something and tell me, is there something special about these pictures? Let me see if you can identify the specialty of these pictures. Of course one point is that except for the bottom center, the you know the pictures that you see are essentially photographs. It does not have wings, yes that is a good observation we are looking at a system that does not require wings. You require wings and an aircraft to generate the lift force but lift force in LTS systems is free of cost without any effort by the presence of the gas inside the envelope which is what we will see now. So good observation there are no wings other than that, yes, yes the shape of them is all more or less same. There are variations in the shape but they are they look very similar, okay. Anything else? Yes. The one on the bottom has only 3 tails as you can see but that is a conceptual sketch. Generally you see a 4 tail structure, 2 vertical, 2 horizontal, okay. I am talking of something more basic or more general than all these technical observations. Yes. No moving parts. No moving parts that is what you think because you do not see anything moving. No, I am asking you to tell me what you see. It is not what you know about what you see. That is the point I wanted to understand. All of these are actual systems which have been developed in IIT Bombay by our students and researchers. So we are talking about a system about which we have some authority and experience. We are not showcasing somebody else's work. We are showcasing our work, okay. That is very important. When I started working in LTS systems in the year 2001, I used to download pictures from the internet and show it in presentations. And in one presentation someone said, okay what have you done? I just said sorry I have just put these things together. From that day onwards I stopped putting pictures from internet and I said let there be a day when we will show a PPT with our pictures. So I am very happy to share with you that in around 12 years, okay, when we started we were 0. The picture that you see on the top left, I will talk about it in more detail. This is during a tech fest of IIT Bombay in 2002. But more about that later, let us look at the first question that always comes in the minds of people who hear about the LTS systems and that is how are they different from the conventional aircraft? So the conventional aircraft, we call them as HTA, heavier than air simply because if I lift an aircraft and if I release it, the aircraft will fall on the ground because it is heavier than air, quite simple. On the other hand, if I lift an LTS system and I release it, what will happen? What do you think will happen? Yes, with your hands so that I can talk to a specific person. What will happen if I lift, for example, if this is an LTS system, I lift it up and if I release it, what will happen? Yes, please. What is your name? Whip in. Whip in. What will happen whip into this system? Very good. Whether it will remain where you leave it or it will go up, correct, because it is lighter than air. If it is a perfectly balanced system, then we should say equal to air in a way, then it will remain where it is. Such systems are called as neutrally buoyant LTS systems, very funny language, neutrally buoyant lighter than air systems. So, the word LTA is only applicable to those systems that use some kind of buoyancy as the main lifting force, but actually they will be heavier or equal to or lighter than the air. Got it? So, you are right. It will remain at this place if it is neutrally buoyant or it will go up. Now, what would you normally prefer in a system, in an aircraft? Would you prefer it to be heavier than air, lighter than air or neutrally buoyant? You want to shift between these three, why would you like to shift? Okay, so because you want to move, you want to change position, sometimes you want to be heavier than air, sometimes lighter than air and sometimes neutrally buoyant, okay. This is a fairly acceptable answer. In general, if you are making an airship, I would prefer it to be heavier than air. What do you think is the reason? If something goes wrong, I want it to come down to me and not hang up in the air and then I am wondering what to do, how to bring it down, okay. So although we make lighter than air systems, in reality we fly them to be slightly heavier than air. And how heavy it is compared to its weight, there is a term for it, it is called as static heaviness. But now in front of you you have two boxes containing the names of the two systems and now not very clear, you will find that on the left hand side we have the lighter than air systems, there are three green boxes and then there are two red boxes, okay. Red boxes are undesirable, green are desirable and since we are doing a course on LTA systems, we are biased in favour of LTA systems, so there are three green boxes and two red boxes, okay. On the other hand, to balance, to make the balance, there are three red boxes on heavier than air systems and two green boxes, but these two red boxes on LTA systems are the basic reason why we do not see them so often. These are very, very serious limitations, except especially the last box. So what are the benefits first, benefits are that you get aerostatic lift, that means you get lift even when they are stationary plus you also get additional lift when they move. So airship being a large aerodynamic body, when the airship moves in the air, it will generate some lift because of its shape. That lift is called a dynamic lift, that is 0 at 0 velocity or it is 0 at 0 relative velocity between the body and the ambient air. So that dynamic lift is an extra thing, you cannot depend on it because it is not always available. Secondly, since they have aerodynamic lift, they do not have to do lot of work to generate force to overcome gravity, therefore they consume less fuel. You can assume that a typical aircraft does two things. It does some work to create force to overcome weight and then it has extra work to create force to give propulsion. In LTA system the first one is free. So the force, the power required to create the force for forward motion is just to overcome the drag, weight is taken care by nature. So if there is less work, less consumption of fuel, more fuel efficient and also as you will realize that many people also mention no moving parts because they thought there are no moving parts. Basically there are few moving parts and they are very simple. Aircraft are far more complex because the same wing has to do many things. Here we are delinked, there is no wing here but then there is a problem. These are bulky bodies because they need volume to generate lift and volume and large size makes you bulky and the best example of that by the way. So therefore they are slow, they cannot fly very far. You cannot expect to have a hypersonic airship, not even supersonic, not even high subsonic. Airships will only be low subsonic. Well unless you go into an outer space and you get Mach number simply because of density and just talking purely of velocity, airships will always be low speed. The maximum Mach number of airships tends to be 0.2, 0.25 may be. So these are low speed vehicles and because they are bulky and because they are buoyant, they are very highly susceptible to disturbances that happen in the atmosphere due to weather changes. So if I have steady wind blowing, there is not much of a problem. I can fight it by giving a power plan. The problem in LTO systems is if the wind changes direction rapidly, then this body is going to also move in response to the disturbances and to create forces that can cancel out the disturbances completely requires a lot of effort and lot of weight. And maybe beyond the point you just cannot do it, you have to simply ground the vehicle and store it. In extreme cases deflate it. So that is a serious limitation. It can never become an all-weather vehicle. It is only going to be a fair weather vehicle and this is one reason why you will never see an airship being used for regular transportation between 2 places. However efficient it is, however low consumption of fuel it can boast. One of the most important aspects, can you answer this question? What is the most important aspect in a transportation system from the customer point of view? Safety is one. Airships are not unsafe. That is the wrong notion. I will dispel it very soon. Do not think airships are unsafe. Safety wise we can tackle safety. No, I do not want to hear murmurs, I want to see hands. Comfort. So, do you think airships are uncomfortable? I will not agree to this, they are not uncomfortable if the weather is comfortable, if the weather is okay. Yes. So, customers want to travel fast. Correct. They, people want to travel fast and airships cannot go beyond a particular speed. However, there is one advantage of airships which other aircraft do not, we will see it. Yeah, they, I cannot say they can land anywhere, it is okay, they hover, they can hover, they can hover, but that does not mean they can land anywhere.